Offen



A. OFFEN Feb. 14. 1956 LAPS 5 Sheets-Sheet 1 Filed Jan. 1a, 1955,Ihvenivr. gAri/zurO/fen g m/FM Feb. 14, 1956 A. OFFEN 2,734,318

LAPS Filed Jan. 13, 1953 5 Sheets-Sheet 2 lnverzi'or. Arthur Offt'n Feb.14, 1956 A. OFFEN 2,734,318

LAPS

Filed Jan. 13, 1953 5 Sheets-Sheet 3 In yen for.

Feb. 14, 1956 OFFEN 2,734,318

LAPS

Filed Jan. 13, 1955 5 Sheets-Sheet 4 In ran to r.

Arthur Offen Feb. 14, 1956 A. OFFEN 2,734,318

LAPS

Filed Jan. 13, 1955 5 Sheets-Sheet 5 Inventor. .Hri-huz Offen UnitedStates Patent LAPS Arthur Olien, South Nutfield, England, assignor toArthur Often Developments Limited, London, England, a British companyApplication January 13, 1953, Serial No. 331,040

6 Claims. (Cl. 51--92) This invention concerns improvements relating tolapping.

The main object of the invention is to provide an improved method of,and apparatus for, internally lapping small round cylindrical holes,especially those of relatively great length.

The holes to be lapped may be as small as ,4 inch in diameter.

The invention is, however, also capable of application to the internallapping of larger round holes and to the external lapping of roundparts. The round surfaces to be lapped may be of cylindrical or of taperformation.

The present invention provides a method of lapping a round surface of awork-piece, comprising the steps of positioning a coiled lap elementcoaxially with the round surface, with one or more coils in contact withthe round surface, and producing relative rotation of the lapelement andthe work-piece about the axis of the lap element so as to producelapping of the round surface by the coil or coils.

The method preferably includes the additional step of reciprocating thelap element and the work-piece relatively along the axis of the lapelement during the lapping operation; and also, for lapping a hole, thepreliminary steps of forming a coiled wire lap element made of resilientmaterial to a diameter greater than the diameter of the hole, applyingan axial tension to the lap element so as to stretch the element andthereby contract the coils to an extent suiiicient to enable the elementto be passed into the hole, and reducing the axial tension on the lapelement so as to increase the diameter of the coils and obtain therequisite resilient pressure of the coils against the surface of thehole for the lapping operation.

The present invention also provides a machine for carrying out themethod comprising the combination of a coiled-wire lap element, a rotarysupport device for each end of the lap element to permit rotation of thelap element about its axis, and driving means for rotating the lapelement about its axis.

The driving means may be connected to both the rotary support deviceswhereby the lap element is driven simultaneously from both ends; but thelap element may be driven from one end only.

The arrangement is preferably such that one at least of the rotarysupport devices is adapted to be displaced in the axial direction of thelap element so as to adjust the tension of that element and thereby thediameter of the lap element coils.

The rotary support device may conveniently be in the form of a chuckfitted to the spindle of a driving motor.

The driving means preferably comprises an air turbine. Very high speedsof rotation are desirable for effective lapping. Speeds of 60,000revolutions a minute can be obtained with an air motor.

The lap element may be made from a length of stiff .resilient wirehaving a portion coiled to serve as a lap- 2,734,318 Patented Feb. 14,1956 See ping surface, and the lapping surface of the coils is providedwith an adherent layer of abrasive material.

The invention is illustrated by way of example in th accompanyingdrawings, in which: 1

Figure 1 is a front elevation of a lapping machine mounted on a stand;

Figure 2 is a side elevation of the machine and stand, with the standand a portion of the machine base sectioned;

Figure 3 is a cross-sectional view on an enlarged scale through themiddle of the head of the machine;

Figure 4 is a cross-sectional view on an enlarged scale through themiddle of the base of the machine;

Figure 5 is an underside view on the line 5-5 of Figure 3;

Figure 6 is a sectional view on the line 6-6 of Figure 5;

Figure 7 is a fragmentary plan view of the blading of the turbine rotor;

Figure 8 is a view showing one way of securing an end of a lap elementto a nipple;

Figure 9 is an elevation, partly in section, of a lap element mounted ona rod;

Figure 10 is a sectional View on the line 1010 of Figure 9, and

Figure 11 is an elevation of another form of lap element.

Referring first to Figures 1 to 7, there is provided a stand 10 fittedfor a platform 11 on which is mounted a lapping machine 12.incorporating a base 13, a head 14, and two side columns 15, 16connecting the head and base.

The middle of the head has a vertical bore 17 in which is slidable acylindrical housing 18 for a rotary driving unit. As shown in Figure 3,the unit incorporates an air turbine provided with a bladed rotor 20fixed on the top end of a vertical spindle 19. The rotor cooperates witha stator 21. On the stator is mounted a dished valve plate 22 ofcircular form. This valve plate is mounted for limited rotaryadjustment. It is fixed on the lower end of an upstanding tube 23, whoseupper end is fitted with a radial arm 24. The tube is mounted forangular movement about its axis to adjust the valve plate, being locatedin a stout tubular post 25 carried by' the housing 18. The post projectsthrough a guide hole 26 in the top of the head.

Compressed air is supplied to the turbine through a; pipe line 27 to aport 28 in a nipple 30 secured to the side of the post 25. Thecompressed air is fed thence down the annular space 31 between the tube23 and the inner wall of the post, passing into a chamber 32 in the topof the driving unit above the valve plate 22.

The valve plate 22 has two diametrically-opposed ports 33. By turning ofthe plate in one or other direction, these ports are brought oppositethe inlet ends of one or other of two pairs of oblique nozzles 34, 35 inthe stator (Figure 5). The nozzles 34 are so arranged as to direct jetsof air in a tangential direction against the blades 29 of the rotor.arranged to direct jets of air tangentially against the backs of theblades, i. e. in the opposite direction, in order to afford a brakingmedium for quickly stopping the rotor.

The spindle 19 rotates in bearings 36 within a dependent neck 37 on thehousing 18 of the rotary driving unit. Exhaust air from the turbinerotor passes into a chamber 38 and thence downwardly through the gapbetween the spindle and a sleeve 40 between which the bearings 36 arelocated. The exhaust air then rises up an annular duct 41 in the neck,and is discharged along radial ducts The other pair of nozzles 35 is Theneck 37 is externally screw-threaded at 44 into a boss 45 having abearing 46 in the bottom of the head. The boss forms part of a rotarysleeve 47. The rim of the sleeve is provided with a dial surface 48. Onthe sleeve is an adjustable ring 49 bearing a scale with a zero mark,whose position is changed by turning the ring. On turning of the dial48, the housing 18 is moved up and down in its bore 17 by thescrew-threaded connection 44. Rotation of the housing is prevented by akey 50 in the head that projects into a vertical slot 51 Within thehousing.

' Fixed on the lower end of the neck 37 is a thrust bearing device 52incorporating a shallow circular chamber 53 housing a rotary disc 54fixed on the lower end of the spindle 19. The bottom face of the disc isof conical formation, and the opposed bottom wall is of correspondingformation. Compressed air is fed into the bottom of the chamber througha port 55 from a pipe line 56 for a purpose to be described later. Thereis a knife-edge leakage path at 57 between the spindle and the bottom ofthe bearing device. There will also be a leakage of air through thenarrow clearance between the rim of the disc and the annular wall of thechamber 53.

The lower end of the. spindle 19 is screw-threaded to receive a chuckdevice 58 for holding the upper end of a lap element 60.

The lap element consists (Figure l) of a length of stiff resilient wirehaving a middle portion 61 wound to helical formation andaxially-disposed ends.

In the base 13 is a vertical bore 62, aligned with the bore 17, andfitted with a vertically slidable housing 63 for a lower rotary drivingunit. The rotary driving unit is an air turbine having the same form asthe upper driving unit in the housing 18, and the same referencenumerals are used for corresponding parts. The lower end of the lap isfixed in a chuck device 58.

The upper portion of the housing 63 projects through the top of thebase, where it is fitted in an annular trough 64 for catching lubricant.

On top of the post 25 on the upper turbine housing 18 is fixed a balancevalve 65 for controlling the supply of pressure air to the inlet port 55of the thrust bearing unit 52. This valve incorporates a cylinder 66 inwhich is vertically slidable a piston 67. The top of the piston isengaged by a coiled return spring 68 fitted within a recess 70 in a cap71 on top of the cylinder. A recess 72 in the bottom of the pistonhouses a coil compression spring 73 which bears upon the top of the tube23 that carries the valve plate 22. An inner pipe 74 for the supply ofoil mist lubricant passes centrally down the tube 23; its upper endpassing through a clearance hole 75 in the middle of the piston 67, andbeing in communication with an inlet port 76 for the supply of oil mistunder pressure. On the lower end of the oil mist tube 74 is a tubularnose 77 which is a free sliding and rotary bit in a central hole withinthe stator 21. In the tip of the nose is a housing for a thrust ball 78.There is a clearance in the thrust ball housing for the passage of oilmist into the turbine housing 18. The ball bears upon a thrust disc 99on the top of the spindle 19.

The opposed walls of the piston and cylinder of the balance valve 65 areprovided with co-operating annular ducts 80, 81. The duct 81 in thecylinder is connected to a port for the supply of pressure air throughthe pipe 56 to the port 55 in the bearing unit. The supply of air to theport 55 is controlled by the extent of the adjustable overlap betweenthe two ducts 80, 81 through up-anddown movement of the piston 67.Pressure air is supplied to the annular duct in the piston through apipe line 82 connected to a source 83 of air pressure.

A similar balance valve 84 is fitted on the bottom end of a post 35 thatprojects downwardly from the turbine housing 63 through the base 13 andplatform 11 into the hollow stand 10. The same reference numerals areused for corresponding parts. A branch pipe 86 for the supply of oilmist from the source 83 is connected to an inlet port 76 in the bottomof the lower balance valve.

When the lap element is fitted to the machine, it is stretched so as tocontract the coils. The pressure of air supplied to the thrust bearingdevice 52 is so adjusted as to first balance the tension of the lap.There is then no load, or but negligent load, on the rolling bearings152.

The balance valves each act to adjust the pressure of air supply appliedto the coned face of the associated thrust disc 54, in such a way thatthe air pressure on the disc is automatically adjusted to counterbalanceany changes in pull on the spindle 19 due to changes in tension by thelap element during the lapping operation. Assuming there is an increasedpull by the lap element, there will be an initial downward movement ofthe upper spindle 19, which carries down the thrust disc 54 and bladedrotor 20. There is a following downward movement of the inner tube 74.In consequence, the piston 67 of the balance valve 65 slides down thecylinder; and the overlap between the two annular ports 80, 81 isincreased, so increasing the supply of pressure air to the chamber 53 ofthe bearing unit 52, until the pull by the lap element iscounterbalanced. Thus the pressure of the lap element against thesurface being lapped is maintained substantially constant and an axialpressure in the machine bearings is reduced or removed. There is acorresponding adjusted compensation effect produced by the lower balancevalve 84 for the lower bearing unit 52.

A lever arm 90 is pivoted under the platform 11 to the back of thestand. This arm extends forwardly, and is coupled by a link 91 to apedal lever 92. The front edge of the pedal lever projects through ahole 93 at the front of the machine, where it is provided with a pedal94. Near its free front end the lever arm 90 is connected by a pull rod95 to the body of the lower balance valve 84. When the pedal 94 isdepressed, the lever arm 90 is drawn down, and this movement produces acorresponding downward movement of the lower balance valve 84. The post85 moves down with the balance valve, so drawing down the housing 63 forthe lower driving unit in its bore 62. The chuck device 58 holding theend of the lap element is thereby pulled down so as to stretch the lapelement and thereby contract the coils.

The forward tip of the lever arm 90 is adapted to be engaged by a stop96 to limit upward movement of that arm. This stop is carried by aslidable handle 97 fitted with pins 98 guided in a support 100. If thepedal 94 is first pushed down, and the handle 97 pulled forward, againsta return spring 101, so as to draw the stop 96 forward, the pedal canthen be released so as to enable the lever arm 90 to move to a fullyraised position at which tension on the lap element is relieved. Thepurpose of this operation will be described later.

The machine is provided with a platform or work-table 102having guides103 at its sides which are slidably fitted on the two columns 15, 16.The work-table has a clearance hole for the lap element. Bellow-shapedgaiters 104 protect the columns and serve as ducts for oil mist. Awork-piece is shown at 105 in dotted lines on the worktable. The lapelement 61 shown is intended for lapping a round hole of cylindricalform in the work-piece. During the lapping operation, the work-table ismoved automatically up and down so as to cause the lap element to movealong the hole while the lap element is rotating. This movement of thework-table is produced by a hydraulic mechanism (shown diagrammatically)which incorporates two piston-and-cylinder devices 110. Oil is suppliedunder pressure alternately to the two ends of each cylinder 111 throughvalves 112 controlled automatically by a trip device 113 operated bystops 114 on one of two vertical piston rods 115 fixed to the sides ofthe worktable 102.

At the back of the machine (see Figures 2 and 3) there is a verticaltubular shaft 'mounted for rotation in a bracket 121 and a bearing 122.At its upper end the shaft is fitted with a radial arm 123 that carriesa pin 124 engaged within a fork 125 at the end of the arm 24. The lowerend of the shaft is fitted with a pair of parallel radial arms 126, 127,connected by a pin 128 which engages a fork 129 on the lower arm 24. Thevalve plates 22 are turned to one or other of their two positions byswivelling the shaft 120 about its axis by a manual control. Thiscontrol consists of an arm 160 on the shaft 120 actuated by a push-pullrod 161 that projects to the front of the machine where it is fittedwith a hand knob 162.

At 130 is a vessel for supplying compressed air with oil mist throughpipe lines 131, 132 to the ports 76 in the two balance valves.

The source of air pressure 83 is connected to the bottom end of a tube133 (see Figure 3) housed within the shaft 120. The two pipe lines 27are connected respectively to the upper and lower ends of this tube. Thetwo pipe lines 82 are also connected to the ends of the tube. There is afurther branch pipe (not shown) for supplying pressure air to the vessel130.

In setting up for a lapping operation, the work-table 102 is lowered,and with the upper end of the lap element 51 fixed in the upper chuck58, the lower end of the lap element is led through the hole in thework-piece 58. The lower end of the lap element is now fixed in lowerchuck 58. The pedal 94 is now depressed, so as to stretch the lapelement, and thereby contract the coils, whereupon the work-table israised in order to bring the coiled portion of the lap within the holeof the work-piece. The petal 94 can now be released to permit expansionof the lap coils against the wall of the hole. The tension is adjustedby turning the dial 48. The turbine motors can now be run to rotate thelap element about its axis for the lapping operation.

It is preferred to fit each end of the lap element with a nipple 134 asshown in Figure 8. The nipple has a shank 135 which is screwed toreceive a coiled end 136 of the wire lap. The nipple is adapted to beengaged in a chuck 58.

The lap element shown in Figures 9 and is intended primarily for lappingblind holes, but it can also be used for lapping open-ended holes. Ahelically-wound wire lap element 140 is mounted co-axially on a rod ormandrel 141, and one wire end is fixed to a boss 142 on one end of therod. The other end of the rod is formed with an integral boss 143, whichis slotted at 144 to receive a sliding blade 145. A sleeve 146 mountedon the boss is internally screw-threaded at 147, and engages screwthreads 148 on the blade. A collar 149 slidable on the rod is secured byscrews 150 to the blade. The collar is connected to the adjacent end ofthe lap element. A thrust bearing 151 is fitted between the adjacentends of the sleeve and boss. When the sleeve is turned, the collarslides along the rod, so adjusting the length of the lap, and therebycontracting or expanding its coils. When using this lap element only onedriving unit may be used, the lap element being adjusted manually.

In Figure 11 is shown another form of lap element incorporating twocoiled wires 160, 161 arranged in the manner of a two-start thread. Thenon-cutting end portions 162, 163 are coiled to a smaller diameter, andpins 164, 165 with nipples are engaged within these coiled ends, wherethey are secured, as by sweating or screwing. There may be three coilsin the form of a threestart coil, or a greater number of coils arrangedin a similar manner. The provision fo two or more coils avoids anypossibility of a one-sided pull at the ends of the element which wouldcause the element to run out of truth. The coiling of the element alongthe full length also affords truer running under tension because of theincreased flexibility.

In the lap element of Figures 9 and 10 an additional coiled wire may beprovided as shown at 166.

The wire from which the lap is made may be of any suitable section, suchas round, square, or rectangular.

6 A convenient section is a round section. This section, however, hasthe disadvantage that it has only a line contact with the surface of thehole. It is therefore advisable to grind or roll a flat on the coils.

In one suitable way of loading the lap element with an abrasive, thesurface is coated electrolytically with a layer of copper. Some suitableabrasive material, such as diamond dust, is pressed into the coating. Itis of importance that the particles shall stand proud of the coils inorder to afford a working clearance for lubricant and swarf. The coilsof the lap are thereafter treated electrically by a reverse process toremove a portion of the copper layer, until the diamond particles areexposed by approximately /5 to /6 of their diameter.

I claim:

1. A lapping machine comprising a lap element, which lap elementcomprises at least one helically-coiled, resilient wire and end membersat the ends of the element connected together by the wire, said wireconstituting the only connection between said end members and providinga lapping surface for the element, support devices gripping said endmembers, reciprocating means for effecting relative movement of thesupport devices in the direction of the axis of the lap element, wherebyan axial tension can be applied to the lap element and its diameterthereby adjusted, supporting means for holding a work-piece to belapped, and means for effecting relative rotation between the lampelement and the supporting means.

2. A lapping machine comprising a lap element, which lap elementcomprises at least one helically-coiled, resilient wire and end membersat the ends of the element connected together by the wire, said wireconstituting the only connection between said end members and providinga lapping surface for the element, rotary support devices gripping saidend members, reciprocating means for effecting relative movement of therotary support devices in the direction of the axis of the lap element,whereby an axial tension can be applied to the lap element and itsdiameter thereby adjusted, driving means for rotating the supportdevices, a thrust bearing for each rotary support device, which thrustbearing comprises a rotary disc-like member connected to the rotarysupport device for rotation therewith and pressure means for subjectingthat face of the disc-like member nearer to the lap element to fluidpressure, thereby counterbalancing the axial pull of the tensioned lapelement, supporting means for holding a work-piece to be lapped, andreciprocating means for moving the supporting means in an axialdirection.

3. A lapping machine as claimed in claim 2 in which throttle means areprovided displaceable by the pull of the lap element to regulate thefluid pressure in accordance with the pull of the lap element.

4. A method of lapping a round surface of a work-piece, comprising thesteps of forming a coiled wire lap element made of resilient materialand having a lapping surface with coils having a radius greater than theradius of curvature of the round surface, gripping the ends of the lapelement and applying an axial tension to the lap element, positioningthe lap element co-axially with the round surface, adjusting the axialtension on the lap element so that'the coils resiliently press on theround surface, and positively rotating both ends of the lap element andthereby producing relative rotation between the lap element and thework-piece.

5. A method as claimed in claim 4 in which the axial tension applied tothe lap element is adjusted during said relative rotation.

6. A method of lapping a round hole in a work-piece, comprising thesteps of forming a coiled wire lap element made of resilient materialand having a lapping surface to a diameter greater than the diameter ofthe hole, gripping the ends of the lap element and applying an axialtension to the lap element so as to stretch the lap element and therebycontract the coils and reduce the diameter of the lap element to anextent suflicient to enable it to be passed into the hole, positioningthe stretched lap element Within the hole, reducing the axial tension ofthe lap element and thereby increasing the diameter of the element sothat it bears against the surface of the 1101c, and positix'ely rotatingboth ends of the lap element and thereby producing relative rotationbetween the lap element and the work-piece.

References Cited'in'the file of this patent UNITED STATES PATENTS 8Soule July 27, Hodgkins Aug. 28, Hedeen Nov. 17, Green Oct. 9, KennedyeMay 22, Stempelin Jan. 22, Johnson July 30, Sam Apr. 7,

FOREIGN PATENTS Great Britain Feb. 10, Great Britain July 25,

